6.1.1 - Cellular Control Flashcards
What is a mutation ?
A mutation is a change in the sequence of bases in DNA
What are the possible causes of changes in the DNA sequence ?
- Insertion - an extra nucleotide is added
- Deletion - a nucleotide is removed
- Substitution
What are the three types of substitution ?
- Nonsense
- Mis-sense
- Silent mutation
What is a nonsense substitution ?
The mutation results in one of the 3 stop codons (TAC, TAT, TGA)
What is a mis-sense substitution ?
Results in a different amino acid sequence being coded for
What is a silent mutation ?
Although it is a different codon, the same amino acid is coded for
What is a point mutation ?
Mutation that occurs because a single nucleotide is changed, added or removed
How can the primary structure be changed due to a mutation ?
- A new codon is formed because of the mutation
- This causes a different amino acid to be coded for
- The different amino acid can cause a change in the primary structure
What is the DNA code said to be ?
- Degenerate
- Non-overlapping
- Universal
How is the DNA code degenerate ?
Lots of different codons code for the same amino acid
How is the DNA code universal ?
The same codon codes for the same amino acid in all organisms
How is the DNA code non-overlapping ?
Each codon is read once, it does not overlap
What is a frameshift mutation ?
The insertion or deletion of a nucleotide or many nucleotides
What can a frameshift mutation lead to ?
- It can lead to the reading frame of the sequence of bases to be moved.
- This will change every successive codon from the point of mutation
What are the three effects of mutations ?
- Neutral effect
- Damaging effect
- Beneficial effect
How can a mutation be neutral ?
- Normal functioning proteins still synthesised
- Phenotype unchanged
How can a mutation be harmful ?
- Proteins not synthesised or are non functional
- Phenotype is negatively impacted
How can a mutation be beneficial ?
Proteins synthesised with a new and useful characteristic in the phenotype
What are the causes of mutations ?
- They can be spontaneous, often during DNA replication
- Rate of mutation can be increased by mutagens
What is a mutagen ?
A chemical, physical or biological agent which causes mutations
Give an example of a physical mutagen
Ionising radiations such as X - Rays
How do ionising radiations have an effect ?
- Break one or both DNA strands
- These breaks can be fixed but mutations can occur along the way
Give an example of a chemical mutagen
Deaminating agents
How does a deaminating agent have an effect ?
Chemically alter bases in DNA such as converting C to U in DNA, changing the base sequence
Give an example of a biological agent
Viruses
How do viruses have an effect ?
Viral DNA may insert itself into a genome, changing the base sequence
What effect can chromosome mutations have ?
- Deletion
- Duplication
- Translocation
- Inversion
What is deletion ?
A section of chromosome breaks off and is lost within the cell
What is duplication ?
Sections get duplicated on a chromosome
What is translocation ?
A section of one chromosome breaks off and joins another non homologous chromosome
What is inversion ?
A section of chromosome breaks off, is reversed, and then joins back onto the chromosome
What are the different ways in which genes can be regulated ?
- Transcriptional
- Post-transcriptional
- Translational
- Post-translation
What is transcriptional regulation ?
Genes can be turned on and off
What is post-transcriptional regulation ?
mRNA can be modified which regulates translation and the types of proteins produced
What is translational regulation ?
Translation can be stopped or started
What is a post-translational regulation ?
Proteins can be modified after synthesis which changes their functions
What are the different mechanisms that can affect the transcription of genes ?
- Histone modification
- Lac operon
- Chromatin remodelling
- Role of Cyclic AMP
What is heterochromatin ?
Tightly wound DNA causing chromosomes to be visible during cell division
What is euchromatin ?
Loosely wound DNA present during interphase
Why is the transcription of genes not able to happen with heterochromatin ?
RNA Polymerase cannot access the genes so transcription can not occur
What does chromatin remodelling prevent ?
It prevents the complex and energy consuming process of protein synthesis from occurring when cells are actually dividing
What can be done to histones to increase or decrease the degree of packing ?
They can be modified
What does acetylation and phosphorylation cause ?
It reduces the positive charge on the histones and this causes DNA to coil less tightly, allowing certain genes to be transcribed
What does methylation cause ?
Makes the histones more hydrophobic so they bind more tightly to each other causing DNA to coil more tightly and preventing the transcription of genes
What does epigenetics mean ?
The control of gene expression by the modification of DNA
What can epigenetics be used for ?
Include all of the different ways in which gene expression is regulated
What are transcriptional factors ?
These are proteins which move in from the cytoplasm and bind to DNA
What do transcriptional factors do ?
They attach RNA polymerase to the DNA
What are activators ?
Start transcription
What are repressors ?
- Stop transcription
- Could also block RNA
How is a gene switched on ?
Hormones activate transcriptional factors, therefore hormones activate genes
How is a gene switched off ?
- The site on the TF that binds to the DNA is blocked by an inhibitor
- This then prevents transcription
What is an operon ?
- A group of genes that are under the control of the same regulatory mechanism are expressed at the same time
- Regulatory gene, operator, promoter and the structural genes
Where are operons more common ?
They are far more common in prokaryotes than eukaryotes
How can operons be useful ?
They are an efficient way of saving resources because if certain gene products are not needed, then all of the genes involved in their production can be switched off
The Lac Operon - genes turned on
Regulatory gene transcribed to mRNA which is translated to make a protein. Lactose joins to that protein and this forms an inactive repressor. RNA polymerase can join the promotor and read the structural gene and then the lactose utilisation genes can be switched on and enzymes for lactose utilisation are made
The Lac Operon - genes turned off
Regulatory gene transcribed to mRNA which is translated to make a protein. That protein is an active repressor and therefore joins to the operator. This means that the RNA polymerase cannot attach to the promotor and enzymes for lactose utilisation are not made
What are the enzymes for lactose utilisation ?
- B - galactosidase (lactose-> glucose + galactose)
- Lactose permease (enables lactose into the cell)
What are the two post transcriptional control ?
- RNA processing
- RNA editing
What is pre-mRNA ?
The product of transcription, it is a precursor molecule
How does pre-mRNA turn into mature mRNA ?
It is modified
What is added to mRNA to stabilise it and delay degradation in the cytoplasm ?
A cap is added to the 5’ end and a tail is added to the 3’ end
How does the cap help the mRNA molecule ?
Aids the binding of the mRNA to ribosomes
What is splicing ?
- Where the RNA is cut at specific points
- Introns are removed and Exons are joined together
What are introns ?
Introns are non coding DNA
What are exons ?
Exons are coding DNA
What is RNA editing ?
Nucleotide sequence of some mRNA molecules can be changed through base addition, deletion or substitution
What effect does RNA editing have ?
Same effects as point mutations and result in the synthesis of different proteins which have different functions
What is the benefit of RNA editing ?
Increases the range of proteins that can be produced from a single mRNA molecule or gene
What is translational control ?
Mechanisms that regulate the process of protein synthesis
What are the mechanisms of translational control ?
- Degradation of mRNA - the more resistant the molecule the longer it will last in the cytoplasm and the more protein will be synthesised
- Binding of inhibitory proteins to mRNA prevents it binding to ribosomes and the synthesis of proteins
- Activation of initiation factors which aid the binding of mRNA to ribosome
What are post-translational controls ?
Controls that involve modifications to the proteins that have been synthesised
What are the mechanisms of post translational control ?
- Addition of non-protein groups
- Modifying amino acids and the formation of bonds such as disulphide bridges
- Folding or shortening of proteins
- Modification of cAMP - it can increase the rate of transcription of the structural genes
What does cAMP(bound to CRP) do to the rate of transcription ?
It increases the rate of transcription
How does cAMP(bound to CRP) increase the rate of transcription ?
- Molecules binds to cell surface membrane
- Triggers the production of cAMP
- cAMP activates proteins by altering their 3D shape
- This could change the active site of an enzyme to become more or less active
What can cAMP also activate ?
Protein kinases
What do protein kinases do to proteins ?
- They catalyse the addition of a phosphate group to a protein
- They can also activate some enzymes, so can act as important regulators of cell activity
What is morphogenesis ?
The regulation of the pattern of anatomical development
What is the homeobox sequence ?
Sequence of 180 base pairs found within genes that are involved in regulating anatomical development in plants, animals and fungi - highly conserved
What does the homeobox sequence code for ?
Homeobox sequences code for homeodomains
What is the homeodomain ?
- This is part of a protein that binds to a TF
- This can activate or repress developmental genes
What are homeobox genes said to be ?
- Regulatory genes
- This is because the homeodomain can bind to DNA and switch other genes on and off
What are hox genes ?
- Subset of homeobox genes found only in animals.
- Involved in the formation of anatomical features in correct locations of the body plan.
- They code for homeodomain proteins.
What are hox genes responsible for ?
Correct positioning of body parts
Where are hox genes found in animals ?
- In gene clusters
- Mammals have four clusters on different chromosomes
How many hox genes do humans have ?
39
What is the order that the genes appear along the chromosome ?
In the order their effects are expressed in the organism
What do hox genes in the head control ?
The development of mouthparts
What do hox genes in the thorax control ?
Wings, limbs or ribs
What are somites ?
They are directed by hox genes to develop in a particular way depending on their position in the sequence
What are the three types of symmetry ?
- Radial symmetry - only top and bottom
- Bilateral symmetry - left and right sides
- Asymmetry - no lines of symmetry
What is apoptosis ?
Apoptosis is programme celled death
What is the role of apoptosis in body plans ?
- It shapes different body parts
- It does this by removing unwanted cells and tissues
What can happen to cells undergoing apoptosis ?
They can release chemical signals which stimulate mitosis and cell proliferation leading to the remodelling of tissues
What does mitosis result in ?
Cell division and proliferation
What is the role of mitosis in body plans ?
To increase the number of cells leading to growth
What regulates mitosis and apoptosis ?
Hox genes
What are the two ways that the expression of regulatory genes can be influenced ?
- Internal factors
- External factors
What are the external factors that can lead to the expression of regulatory genes ?
- Change in temperature
- Change in light intensity
- Pathogen attack
- Drugs
What are the internal factors that can lead to the expression of regulatory genes ?
- Hormones
- Psychological stress
